熔融物堆内滞留(In-vessel retention， IVR)已成为核电厂处理堆芯熔融严重事故的一种有效管理策略。为使IVR成功，既要满足热失效准则，保证反应堆压力容器(Reactor pressure vessel， RPV)的局部热通量低于堆腔内冷却剂的临界热通量(Critical heat flux， CHF)，也要确保RPV的压力边界完整性，避免发生结构失效。为此，需要对CHF下RPV的结构完整性进行分析。对CHF下某堆型的RPV进行热分析，得到了RPV器壁局部熔化后的有效几何模型和沿壁厚的温度分布。进而，考虑热载荷和压力载荷作用，对该RPV模型进行极限载荷分析和IVR 72 h蠕变分析，确定RPV的极限承载能力。结果表明，IVR 初始时刻4.9 MPa内压作用下该RPV最薄器壁径向截面全面屈服，达到对应的极限条件;72 h后3.6 MPa内压下的最大局部蠕变应变为4.1%，而3.7 MPa下则高达42.5%。因此，可将3.6 MPa视为该堆型RPV在CHF工况下72 h内的极限载荷。

The In-vessel retention (IVR) of molten core has been part of the effective management strategies of the severe accidents for nuclear power plant. To make IVR succeed, the thermal failure criterion must be met, so the local heat flux of reactor pressure vessel (RPV) wall should be lower than the critical heat flux (CHF) of the external coolant. Besides, the pressure boundary integrity of the RPV should also be ensured to avoid the structural failure. Accordingly, it’s urgently necessary to analyze the structural integrity of the RPV under CHF. Firstly, the thermal analysis of a RPV under CHF is carried out to obtain effective geometric model with some of the RPV wall molten and temperature distribution along the wall. Then the limit load and IVR 72 hour creep behavior are analyzed for this model subjected to the thermal load and internal pressure, and the ultimate load capacity of the RPV is subsequently determined. The results show that the whole wall along the thinnest thickness of the RPV yields and the RPV reaches the ultimate load capacity under internal pressure of 4.9 MPa at the beginning of the IVR. The maximum local creep strain of 4.1% is reached under 3.6 MPa within 72 hours, while the internal pressure of 3.7 MPa results in a significant increase of maximum creep strain up to 42.5%. Therefore, the ultimate load capacity of this RPV under CHF in 72 hours is determined to be 3.6 MPa.